[Stdlib] Make the SwiftNativeNSXXXBase classes gracefully handle being decoded with NSKeyedUnarchiver.

stdlib/public/stubs/SwiftNativeNSXXXBase.mm.gyb

@@ -62,6 +62,9 @@ SWIFT_RUNTIME_STDLIB_API
 
 @implementation __SwiftNativeNS${Class}Base
 
+- (id)initWithCoder: (NSCoder *)coder {
+  return [self init];
+}
 - (id)retain {
   auto SELF = reinterpret_cast<HeapObject *>(self);
   swift_retain(SELF);

test/Interpreter/SDK/SwiftNativeNSXXXCoding.swift

@@ -0,0 +1,56 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+
+// REQUIRES: objc_interop
+
+import Foundation
+import StdlibUnittest
+
+let testSuite = TestSuite("SwiftNativeNSXXXCoding")
+
+// Ensure that T gracefully handles being decoded. It doesn't have to
+// work, just not crash.
+private func test<T: NSObject & NSCoding>(type: T.Type) {
+  if #available(macOS 10.13, iOS 11.0, tvOS 11.0, watchOS 4.0, *) {
+    let swiftClassName = "__SwiftNative\(type)Base"
+    print(swiftClassName)
+    let archiver = NSKeyedArchiver(requiringSecureCoding: true)
+    archiver.setClassName(swiftClassName, for: T.self)
+    archiver.encode(T(), forKey: "key")
+    archiver.finishEncoding()
+    let d = archiver.encodedData
+
+    let unarchiver = try! NSKeyedUnarchiver(forReadingFrom: d)
+    _ = unarchiver.decodeObject(of: T.self, forKey: "key")
+  }
+}
+
+
+// Test all the classes listed in SwiftNativeNSXXXBase.mm.gyb except for
+// NSEnumerator (which doesn't conform to NSCoding).
+
+testSuite.test("NSArray") {
+  test(type: NSArray.self)
+}
+
+testSuite.test("NSDictionary") {
+  test(type: NSDictionary.self)
+}
+
+testSuite.test("NSSet") {
+  test(type: NSSet.self)
+}
+
+testSuite.test("NSString") {
+  test(type: NSString.self)
+}
+
+testSuite.test("NSData") {
+  test(type: NSData.self)
+}
+
+testSuite.test("NSIndexSet") {
+  test(type: NSIndexSet.self)
+}
+
+runAllTests()